Heat-sensitive stencil paper

ABSTRACT

A heat-sensitive stencil paper consisting of a porous thin paper (Stencil base tissue) laminated to a vinylidene chloride-vinyl chloride copolymer film and a powder layer formed on the surface of said film.

United States Patent [72] Inventors Keishi Kubo Kanagawa-ken; Kiyoshi Sakai, Tokyo; Kenzi ltoh, Tokyo,

HEAT-SENSITIVE STENCIL PAPER 2 Claims, No Drawings U.S.Cl 161/162,

101/1282,ll7/3.4,l17/35.5,117/35.6,156/289, 161/164,161/165, 161/251, 161/406 Int. Cl B41c l/l4, B41m1/12,B44d3/30 Field ofSearch 161/162,

References Cited UNITED STATES PATENTS l/l971 1/1971 2/1971 12/1942 11/1964 7/1965 3/1966 6/1966 9/1966 ll/l966 10/1968 2/1969 1l/1969 Grabovez Dalton.....

Steber et al.....

Urancken Primary Examiner-Harold Ansher Attorney-Woodhams, Blanchard and Flynn 101/128.2 101/128.4 ll7/l.7 161/162 117/l.7 161/162 l56/289X 161/164 1l7/36.7X 1l7/36.9 117/1.7X 161/164 101/128.2 ll7/36.7 l17/35.6X 117/35.6X

ABSTRACT: A heat-sensitive stencil paper consisting of a porous thin paper (Stencil base tissue) laminated to a vinylidene chloride-vinyl chloride copolymer film and a powder layer formed on the surface ofsaid film.

HEAT-SENSITIVE STENCIL PAPER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to heat-sensitive stencil paper consisting of a porous thin paper (stencil base tissue) laminated to a vinylidene chloride-vinyl chloride copolymer film with a powder'layer formed on the surface of the film.

2. Description of the Prior Art The inventors previously developed a heat-sensitive stencil paper prepared by laminating adhesively a vinylidene chloride-vinyl chloride copolymer film upon a porous thin paper (stencil base tissue). In order to make a stencil master from the stencil paper, the original is placed on the film surface of the stencil, infrared rays are irradiated through the porous thin paper, whereby the areas of the resin film corresponding to the image areas of the original melt so as to form perforations corresponding to said image areas, and then the original is removed. Thus a stencil master whose film has been perforated with a desired image is obtained. When a copy sheet to be printed is placed on the perforated surface of the thus obtained stencil master and a printing ink is applied to the surface of the thin paper, the ink permeates through the thin paper and is applied to the copy sheet through the perforated parts and forms a print image on the copy sheet.

It has not yet been made clear how the perforations are formed during the process of preparing the aforementioned stencil master; however, we assume that the perforation takes place probably, based on the mechanical procedures mentioned below. The infrared rays pass through the tissue paper, the adhesive layer, the film and finally reach the original, whereupon the image areas of the original absorb the infrared rays rapidly to elevate the temperature thereof as well as, due to heat transfer, to increase the temperature of the parts of the resinous film corresponding to the original image. Said parts of the film soften and shrink until cutting of the film occurs around the centers thereof and finally perforations are formed. However, in reality, a part of the resin of the film melts and sticks to the original image or to the perforated part of the stencil master paper, thus not only damaging the image part of the original when the original is separated from the obtained stencil master but also filling up the perforated part of the master to prevent printing ink from passing through the perforations. Printing by the use of such damaged stencil master results in a printed image which is lacking clearness and resolving power. In order to prevent these unsatisfactory results, it is first of all necessary to prevent the melted resin from sticking fast to the original. To achieve this purpose, it may be recommended to use various means of keeping the film and the original from contacting closely together, such as by putting, for example, some releasing substance between them. To give a known example, this principle is similar to a method (Japanese Pat. Publication No. show a 34-3236) wherein powder is used to prevent them from sticking together when manufacturing a film of vinylidene chloride which has self-tackiness (for instance, films known under the trade names of Saran Wrap, Kure Wrap," etc., used for packing foods in refrigerator). However, a releasing substance useful in the present invention must be one which has a relatively higher melting point, is heat-conductive and has an excellent infrared ray permeability.

SUMMARY OF THE INVENTION Based on the foregoing knowledge, the inventors have conducted elaborate investigations and finally discovered that colorless, or yellow, or red fine powder is satisfactorily suited for use as a releasing substance. Accordingly, the object of the present invention is to provide a heat-sensitive stencil paper prepared by dispersing a releasing substance uniformly over the surface of a vinylidene chloride-vinyl chloride copolymer film.

This invention relates to a heat-sensitive stencil paper consisting of a porous thin paper (stencil base tissue) laminated to a vinylidene chloride-vinyl chloride copolymer film, in which the improvement comprises providing a powder layer on the surface of said film.

As the properties required for for powders suitable for use as a releasing substance as stipulated in the description of the present invention, the powder should not absorb electromagnetic waves within a wavelength range of approximately 700-2,000 my. to a great extent, it should not melt at a temperature below 200 C. and melt-stick to a copy sheet and a printing ink, and it should not decompose and produce an unpleasant smell or poisonous gas. Any powder that satisfies all the described foregoing requirements is good enough to be used for the purpose. For instance, such powders as talc, starch, mica, silica, calcium carbonate, and alumina are particularly suitable. The diameter of the powder particles should be below 0.2 mm., and preferably between 0.5 and 50p When a powder having a particle diameter larger than 0.2 mm. is used, the space between the original and the film of the stencil master increases too much and reduces the heat conductivity required at the time of forming the perforations. By increasing the quantity of the powder applied to the surface of the film, the effect on the releasing property becomes better; however, the use of an excess of the powder leads to deceased heat conductivity just as in the case ofa powder having too large a particle diameter. It has been found from the results of experiments that the suitable quantity of the powder to be coated on the surface of the film is approximately 3.0g./m. or less, although the optimum quantity differs with the kind, specific gravity, etc. of the powder. The heat sensitivity of the stencil master paper under the aforementioned conditions is not influenced by the coating of the powder on the surface of the film. Therefore the time required for exposure to infrared rays in the case of a stencil master prepared according to the present invention is equal to that of the conventional ones. In manufacturing a stencil paper according to this invention, it is preferred that the powder coating is applied after the film and the thin porous paper are adhered together and then dried; however, the powder coating may be applied during the step of film-manufacturing or the like.

The invention will be further illustrated concretely by the following examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 An ordinary vinylidene chloride-vinyl chloride copolymer film (the composition ratio is -95 20-5) having a thickness of 7a was at first heat-treated at a temperature of C. under tension. The film was then laminated with a porous thin' paper (stencil base tissue) having a thickness of 35p. (Manufactured by Nippon Shigyo Co., Ltd.) by use ofa vinyl acetate adhesive (methanol solution) and dried to prepare a conventional heat-sensitive stencil paper suitable for duplicating. Then an even powder layer was formed on the surface of the film by applying talc powder (prepared by reducing the usual reagent talc to fine powder in a mortar) having an particle diameter of about 5-20p. with rubbing to obtain the desired heat-sensitive stencil paper for duplicating.

Example 2 A heat-sensitive stencil master for duplicating was obtained by forming an even powder layer by the application of silica powder (manufactured by Shionogi Pharmaceutical Co., Ltd. under the trade name ofCarplex") having a particle diameter of l-5,u. with rubbing to the surface of the film of an ordinary heat-sensitive stencil paper as used in example 1.

In order to compare the performances of a heat-sensitive stencil paper obtained according to the present invention with that of a conventional stencil paper, an original (a piece of newspaper) was respectively placed closely on the powder layer formed on the film surface of the stencil paper prepared according to the present invention and on the surface of the film of a control stencil paper, both were exposed to infrared rays from the side of the thin paper layer thereof to form perforations corresponding to the original image. The originals were removed from the resulting respective stencil papers which were then clamped on the cylinder of a rotary stencil duplicator and prints were run (by use of an emulsion type duplicating ink), the results of which are as follows.

In the case of the control stencil paper, the image part of the original was damaged at the time when the original was separated from the stencil master after the exposure to infrared rays because the thick letters and the solid part of the original were fused with the surface of the film. In the copying operation, the aforementioned fused part prevented the ink from passing through perfectly and no satisfactory prints were obtained and there were some places on the printed sheets where no impression was produced. Where fine letters were stencilized, very small fused areas were found and no perfect lines were reproduced along the edges of the image, which resulted in a lack of clearness or sharpness of the image and the image was very poorly copied.

While in the case of a stencil master prepared according to the present invention, such troubles as mentioned in the foregoing did not occur at the time of separating the original from the stencil master. The separation was always easy and no fusing of the resinous film to the original or perforated parts was observed at all. The seeping of the ink was also very satisfactory and the reproduced image was accordingly so clear that more than 2000 printed sheets bearing an image of excellent resolving power were obtained.

What is claimed is:

l. A heat-sensitive stencil paper comprising a thin film layer consisting essentially of vinylidene chloride-vinyl chloride copolymer resin and capable of being perforated by heat from infrared radiation absorbed by image areas on an original placed in contact with one face of said film layer, the other face of said film layer being laminated to a porous thin paper layer capable of transmitting a fluent ink to said film layer, said one face of said film layer being coated by an adhering continuous powder layer of uniform thickness applied at a rate of not in excess of about 3.0g./m. based on the treated area of said one face of said film, and consisting of a powder selected from the group consisting of talc, starch, mica, silica, calcium carbonate and alumina, said powder having a particle size of less than 0.2mm.

l. A heat-sensitive stencil paper according to claim 1, in which the powder has a particle size in the range ofO.5 to 50p. 

2. A heat-sensitive stencil paper according to claim 1, in which the powder has a particle size in the range of 0.5 to 50 Mu . 